A Practical Oven-Aging Method for Evaluating Long-Term Cracking Performance of Asphalt Mixtures in Virginia

About the report:

The Virginia Department of Transportation (VDOT) has adopted the balanced mix design (BMD) framework to enhance the durability and service life of its dense-graded asphalt surface mixtures with A and D designations. VDOT’s BMD framework incorporates the indirect tensile cracking test to assess the cracking susceptibility of asphalt mixtures through the cracking tolerance (CT) index under short-term oven-aging conditions. However, the current framework does not consider the effect of oxidative aging on asphalt mixture performance throughout its service life, which can be evaluated using long-term oven-aging (LTOA) methods.

This study aimed to develop a practical LTOA method for inclusion in VDOT’s BMD framework and establish a preliminary performance criterion for the CT index during the mix design and production phases. The research involved 10 dense-graded asphalt surface mixtures with varying reclaimed asphalt pavement contents and binder grades. Laboratory-produced and plant-produced mixtures were subjected to oven-aging at two different temperatures (i.e., 95°C and compaction temperature) to determine the appropriate aging durations for each temperature conditioning method. The study evaluated the changes in mixture performance characteristics using the CT index and examined the corresponding changes in asphalt binder rheological and chemical properties across various aging durations.

The study showed that the CT index effectively captures the anticipated behavior of asphalt mixtures undergoing laboratory oven-aging. As mixtures age, their performance rankings shift, highlighting distinct resistance characteristics that can be assessed through long-term performance evaluations. The research suggests that laboratory oven-aging at 95°C can be used for shorter durations to gauge long-term performance effectively. Furthermore, aging at the compaction temperature provides results equivalent to 95°C, supported by consistent binder characteristics. For VDOT’s dense-graded surface asphalt mixtures with A and D designations, a 6-hour oven-aging duration at compaction temperature is recommended for the design phase, with a preliminary CT index threshold of 55. In addition, an oven-aging duration of 2 hours at compaction temperature following reheating during production and 4 hours at compaction temperature for non-reheat conditions (i.e., hot compacted) are deemed suitable for evaluating the long-term performance of asphalt mixtures during production, with a preliminary CT index threshold of 55 for both cases.

The study recommends that VDOT’s Material Division adopt the LTOA method and the associated CT index threshold developed in this study for the design phase of asphalt mixtures into its BMD specification. In addition, the study recommends a follow up study to evaluate the viability of using the LTOA method and the CT index threshold during production, both for reheat and non-reheat conditions.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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